This an outcrop from a spillway in Arkansas that cuts through a thick section of Pennsylvanian turbidites. You are looking at the bedding surface of greywacke that had a shale layer overlying it. The shale and overlying sandstone have been eroded. This bed of greywacke is dissected by joints, sets of simple planar fractures with a common orientation. You should note and trace: 1) representative fractures of the joint sets, distinguishing in some manner one from the other, and 2) T junctions where one joint terminates against the other.

Questions that might arise include the following. How many joint sets are there? What is the angle between the joint sets? Do members of one set tend to truncate in T junctions against the other?